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Abstract

Increased levels of reactive oxygen species cause senescence and cell death, and thus are proposed to be a major contributor to aging. Sir2, a class III histone deacetylase, extends the lifespan/survival of many organisms. To better understand the mechanism by which Sir2 counteracts aging, we investigated the effect of Sir2α, the murine ortholog of Sir2, on cell death by oxidative stress in the heart. Treatment of cardiac myocytes (CMs) with H2O2 (50 μM) for 24 h induced a 1.5 fold (p<0.05) increase in cytoplasmic accumulation of mono- and oligo-nucleosomes, indicating induction of apoptosis. H2O2 treatment significantly upregulated Sir2α (1.6 fold, p<0.05) in CMs. Downregulation of Sir2αby adenovirus harboring Sir2α-shRNA significantly increased H2O2-induced apoptosis (1.8 fold, p<0.05), suggesting that Sir2α plays a protective role against oxidative stress. Transduction of CMs with adenovirus harboring Sir2α, but not dominant negative (DN)-Sir2α, significantly increased expression of catalase (2.0 fold, p<0.05), an anti-oxidant. The activity of catalase-luciferase reporter gene was also stimulated by Sir2α (1.5 fold, p<0.05), but not by DN- Sir2α. H2O2 increased catalase expression by 1.4 fold (P<0.05), while H2O2-induced upregulation of catalase was inhibited in the presence of Sir2α-shRNA. In order to examine whether Sir2α exhibits protective actions against oxidative stress in vivo, we treated cardiac-specific Sir2α transgenic mice (Tg- Sir2α) with paraquat (PQ, 10 μg/kg), an inducer of oxidative stress, for 2 weeks. Although PQ treatment significantly reduced left ventricular ejection fraction and % fractional shortening in non-transgenic (NTg) mice (61, 27%), cardiac function was maintained in Tg- Sir2α after PQ treatment (70%, p<0.05; 32%, P<0.05). TUNEL staining revealed a significantly elevated level of apoptotic cells in NTg hearts (2.0 fold, p<0.05) but not in Tg- Sir2α hearts. Although PQ increased catalase expression in NTg and Tg- Sir2α hearts, the level of catalase was significantly higher in Tg- Sir2α heart (1.6 fold, p<0.05). These results suggest that Sir2α protects CMs from apoptosis in response to oxidative stress in part through upregulation of anti-oxidants, such as catalase, in the heart.